How am I looking?

[Mr.Rocc]

I only have inverts copepods and a watchman goby in the tank. I have about 45 lbs of LR and 40lbs of live sand. I know my Ca and Mg are low and will be dosing 2 part soon. How am I looking?

 

[JimWelsh]

That Ca value is hard-to-believe low. How are you measuring it? What number do you get if you test your newly-made saltwater for Ca?

 

[Mr.Rocc]

I just got the pro kit but I think I did f up the test cause I got impatient. I think I'll retest it.

 

[Randy Holmes-Farley]

What salt mix are you using?

 

[Mr.Rocc]

I use water from my local fish store since my water around my house is absolutely horrid.

 

[BoneXriffic]

I use water from my local fish store since my water around my house is absolutely horrid.

Not to jump on randys toes. But you get ro from them and mix your own salt in or by premix from lfs?

 

[jman9331]

What test kit are you using?

 

[Mr.Rocc]

Premix

 

[Randy Holmes-Farley]

Have you ever tested it directly?

 

[Mr.Rocc]

No but I can when I get homr

 

[Mr.Rocc]

Premix from LFS is about 300 ppm Ca

 

[Mr.Rocc]

Unless I'm just using my test completely wrong. I have the red sea pro kit. I add 5 ml of salt water, 5 drops of the stuff, shake it for 10 seconds, add a scoop of that other stuff, shake that for 20 seconds, get 1 ml of Ca solution and add it till it turns blue. Am I doing anything wrong?

 

[JimWelsh]

Taking your statements at face value, combined with the Red Sea Calcium Pro test kit instructions, then both your tank water and the water from the LFS take between 0.58 and 0.60 mL of titrant to get the solution to turn blue. If this is true, then either the LFS is supplying Ca deficient water, or there is some test kit error.

While test kit error is a possibility, it would require that the titrant were somehow more concentrated than it was supposed to be, which is an unlikely event, unless perhaps it had been left open for some considerable time, and allowed to become concentrated due to evaporation.

An EDTA titration of calcium is a rather straightforward thing. The first 5 drops of reagent are a hydroxide to precipitate magnesium. Either that works well, or it doesn't. If it doesn't, the the net effect is to leave some Mg in solution, which will make the Ca reading artificially higher than it should be, but not make it read low. The powdered reagent is just an indicator dye, and as long as you can see the color well, then it is hard to get the amount wrong; the amount used won't affect the reading. The third reagent is the titrant, and the amount of titrant needed to make the solution turn blue is directly related to the relative proportions of the amount of sample times the Ca concentration in the sample vs. the concentration of EDTA in the titrant. The more sample and/or the more Ca in the sample, then the more titrant it takes to make the vial turn blue. Conversely, the more concentrated the EDTA is in the titrant, then the less titrant it takes to make the vial turn blue. So, the accuracy of such a Ca test kit relies upon (1) complete Mg precipitation by the hydroxide, (2) accurate measurement of the amount of sample, and (3) accurate concentration of the EDTA titrant. The only test kit errors that could make a reading artificially low is if the amount of sample was smaller than it was supposed to be, or if the concentration of the EDTA titrant is higher than it was supposed to be.

 

[Mr.Rocc]

Well I retested it and got 325ppm the fish store says they use salt that has 350ppm calc so I think I need to start making my own SW

 

[Randy Holmes-Farley]

That's a good idea, IMO. You can boost what you have now with calcium chloride.